This invention relates to the production of a large diameter multi-layer plastic pipe from helically coiled plastic strips. More particularly, this invention relates to the production of such pipes which have an ultraviolet light-protecting outer surface and light-reflecting inner surface.
Production of plastic pipes by helical-seam techniques have gained increasing interest. For example, a plastic strip can be fed tangentially to a cylindrical mandrel at an angle to the axis thereof so that the strip is coiled in a multiplicity of successive turns on the mandrel with confronting edges of the successive turns being bonded together.
Generally, helical-seam techniques have been used to produce large diameter plastic pipes, (e.g., generally from about 0.5 meters to about 3 meters in diameter) such as sewage, water pipes, or the like and including maintenance holes or manholes which give access to such pipes. Once such pipes are in use, it is in many cases required that a utility or surface inspection thereof include a visual or video viewing and/or a video recording of the interior of the pipe. Traditionally, such pipes have been made utilizing a black, high density polyethylene (HDPE) because of the black HDPE pipe's excellent resistance to deterioration due to ultraviolet light. However, the black interior of the black HDPE pipe makes it unsuitable for video inspection of the interior due to light absorption properties of the black color.